This invention relates to an apparatus for filtering contaminated liquids, particularly cooling and/or lubricating liquids which are employed during the machining of workpieces with metal removal, comprising a liquid container with an inlet for contaminated liquid and an outflow for filtered liquid, in which container a filtering insert is disposed which can be connected to the outflow.
Apparatuses of this type, which are also sometimes termed sieve separators, are employed during the machining of workpieces with metal removal for the conditioning of cooling and lubricating liquids which are used in grinding, turning, milling, etc, and which have to be freed from material swarf and dust as extensively as possible before they can be reused as cooling lubricants. Contaminated liquid reaches the liquid container via the inlet and is taken off as purified liquid via the outflow after it has flowed through the filtering insert, which retains swarf and dust from the liquid. The separated contaminants can be automatically removed by means of an extractor device. If the amount of contaminants which arise is small, it is also possible for the liquid to be discharged from the filtering apparatus and for the sludge which has accumulated over the course of time to be removed by hand.
An apparatus of the type cited at the outset is known from DE 196 35 364 A1, in which a bar screen is disposed in the liquid container as a filtering insert, the inlet side of which is directed downwards, wherein the scraper chain of a scraper conveyor is led past the inlet side of the bar screen in order to clean the bar screen. In this known apparatus, the area of the bar screen through which the liquid can flow during filtration is limited and is restricted by the length and width of the liquid container. Since the space taken up by filtering apparatuses in the vicinity of machine tools should be designed to be as small as possible, and a compact mode of construction of the filtering apparatus is therefore required, this known apparatus is in most cases unsuitable for full-flow filtration, in which the entire liquid is filtered at a constant degree of fineness. Consequently, it is generally only used for partial flow filtration in which only part of the liquid is finely filtered through the bar screen using an aperture width of 50 xcexcm or 75 xcexcm, whilst the remainder of the liquid to be purified is deemed to be satisfactory with somewhat inferior degree of filtration which can be achieved via a further, coarser filter, or which can be achieved by means of a stack of plates which results in calming of the flow, as a result of which contaminants which are entrained in suspension are able to settle in the contaminated liquid.
For throughputs comprising larger amounts of liquid which have to be finely filtered by full-flow filtration, apparatuses are known in which a filtering insert which rotates about a horizontal axis is disposed immersed in the liquid. The contaminated liquid flows into the interior of the drum through a filter means disposed at the periphery of the filtering insert and is discharged via a suction pipe connected to the insert. At least one scraper is disposed in the container parallel to the axis of rotation of the drum and is pressed against the insert, and when the scraper rotates it removes contaminants which have been deposited on the filter means. These contaminants then sink downwards in the liquid container and are removed from the container by a rake apparatus.
In this known apparatus for full-flow fine filtration, the discharge of the filtrate from the interior of the filtering insert frequently causes problems, since the suction pipe is led via a rotary lead-through into the interior of the filter, which is difficult to seal from the contaminated liquid. In this known apparatus, only a comparatively small pressure difference can be employed between the interior of the filter and the liquid on the outside thereof, so that intermediate storage of the filtrate in a filtrate tank directly behind the filtering insert is necessary. From the filtrate tank, the filtrate can be fed back to the machine tool or the like by means of feed pumps. In this known apparatus it has proved particularly difficult to install and remove the filtering insert. These are operations which have to be carried out at regular intervals in order to subject the filter to a thorough cleaning procedure if contaminants which have not been removed by the scraper have blocked the filter means of the insert over the course of time.
The object of the present invention is to improve an apparatus of the type cited at the outset so that a high throughput of liquid through the filtering insert is achieved for an apparatus of comparatively small external dimensions, wherein it should be possible to take off the filtrate directly from the liquid container without additional filtrate collecting vessels, and wherein it should be possible in addition to ensure reliable cleaning of the filtering insert in operation, and to ensure ease of replacement of the filtering insert.
This object is achieved according to the invention by providing a filtering insert which substantially consists of a filter drum which can be installed in the liquid container fixed in relation thereto and which comprises a filter means which is disposed at its periphery and which can be cleaned by a cleaning device which can be moved along the peripheral face of the drum. The filter drum is preferably cylindrical and is disposed suspended or standing on an end face in the liquid container, and can be inserted therein from above and can be removed from the container from above.
The use of a filter drum at the periphery of which the filter means is disposed results in a large filter area which is sufficient even for high liquid throughputs. Since the filter drum itself does not rotate in the liquid container, but is fixedly disposed in relation thereto, the costly rotary lead-through which was used in the prior art between the interior of the filter drum and the take-off pipe for the filtrate can be dispensed with. Instead, it is possible to attach and seal the pipe for the filtrate fixedly to the filter drum by a flange or by another means, and to remove the filtrate directly from the interior of the filter drum by means of a feed pump. A relatively large pressure drop can thereby be achieved between the outside and the inside of the filter, which results in a high throughput through the available filter area.
Since the filter drum can be removed from the container from above, and can be inserted in the latter from above, the liquid of the liquid container does not need to be discharged when the filter drum is replaced, so that the down-time of the apparatus when changing the drum can be kept to a minimum. The drum can be replaced within a few minutes, by detaching it from the flanged joint to the feed pump, pulling it upwards from the container together with part of the suction line, and replacing it by a new drum, which then only has to be flanged to the feed pump before it can be put in operation. Outflow of the filtrate advantageously occurs via a filtrate suction pipe which projects into the drum interior and which is sealed by an end face of the filter drum. At the same time, the arrangement can be designed so that the filter drum is disposed suspended on the filtrate outflow, and so that no additional fixing means are therefore necessary for the fixed mounting thereof in the interior of the liquid container.
The filter drum can have a discharge opening on its bottom end face, which discharge opening can be opened or closed from the top end face. In order to remove the filter drum, which is necessary for the replacement thereof or for a thorough cleaning operation, the discharge opening on the bottom end face can be opened from the top face of the drum, so that any filtrate which still remains in the interior of the drum can drain downwards therefrom when the drum is lifted upwards out of the liquid container. To facilitate thorough cleaning of the drum, which is carried out subsequently to the removal thereof, the drum advantageously has a closable cleaning aperture on its top and/or bottom end face. After opening the cleaning aperture, the interior of the drum is accessible in order to clean the interior space of the drum with a high-pressure cleaning device, for example.
The filter means at the periphery of the filter drum is advantageously a bar screen, which is subjected to practically no abrasion and which can be cleaned particularly easily. In order to clean the filter means when the filter is in operation, the cleaning device preferably comprises at least one cleaning element which extends over the height of the filter drum and which can be moved round the filter drum periphery along the filter means. The entire cleaning device is preferably mounted on the top face of the container so that it is immersed therein, and is advantageously rotatably mounted on the container top face by means of a pivot bearing. The cleaning device can then be moved around the fixedly disposed filter drum by means of a suitable drive motor, whereupon the cleaning element or elements is/are moved along the peripheral face of the drum and at the same time remove contaminants which have been deposited there. Each cleaning element advantageously consists substantially of a scraper- and/or brush strip which can be moved along the filter means.
It is particularly advantageous if the cleaning element is mounted replaceably on the cleaning device. If wear has occurred, it can then easily be replaced by a new cleaning element, and it is also possible to use cleaning elements which ensure the best possible cleaning effect for the type of contamination which occurs in each case for different contaminants in the liquid, such as grinding dust or turning, milling or shaving swarf for example. The cleaning element can preferably be removed from or installed in the cleaning device from the top face of the container, and can therefore be replaced without it being necessary to drain off liquid from the liquid container in order to obtain access to the cleaning element.
The cleaning device preferably comprises a plurality of cleaning elements which are disposed on a common retaining ring surrounding the filter drum, preferably at a uniform spacing from each other. Due to the uniform arrangement of a plurality of cleaning elements which all clean the filter means of the filter simultaneously, the contact pressure forces which are exerted by the cleaning elements on the drum cancel each other out, so that the drum is securely fixed within the container even when it is merely suspended via the outflow to which is flanged, and is not subjected to a load which acts radially on it.
In one particularly advantageous embodiment of the invention, the filter drum or the suspension thereof and the cleaning device are disposed on a common cover of the liquid container. This arrangement even makes it possible to equip existing liquid containers with the filter drum and the associated cleaning device according to the invention, simply by suspending them from above in a liquid container which has been freed from its previous built-in filter components, wherein the common cover can be supported at the top edge of container. The filter means disposed at the periphery of the filter drum is preferably completely immersed in the liquid to be filtered in the liquid container, so that the feed pump which is connected to the suction line is reliably prevented from completely removing by suction the filtrate which is present in the interior of the filter drum. In order to ensure the permanent, complete immersion of the filter drum in the liquid during the operation of the filtering apparatus, a level switch is advantageously disposed in the liquid container in the manner known in the arts, and ensures that the feed pump for the liquid is switched off when the liquid level falls below a predetermined level.
The cleaning element is preferably displaceably accommodated in a profiled retaining strip, and is advantageously height-adjustable in relation to the filter drum. The axial displaceability of the cleaning element in the profiled retaining strip enables it to be replaced particularly easily on the occurrence of wear or the like. Said height-adjustability in relation to the filter drum is capable of further improving the result of cleaning the filter means when the latter is swept, since cleaning is thereby not only effected in the peripheral direction of the filter drum, but is also effected in the axial direction thereof, whereby it is ensured that contaminants such as swarf, for example, which have settled in the apertures of the filter means which is designed as a bar screen, are completely pulled out of the apertures again or are at least sheared off, and it is thereby possible to create a smooth surface on the filter means on which further contaminants cannot easily deposit.
For some purposes of use, the apparatus according to the invention preferably comprises a flushing device for the filter drum, which device substantially consists, for example, of a backflushing pump which delivers into the interior of the filter drum. It is also possible for at least one of the cleaning elements to be operated with a pressure cleaning unit which can be acted upon by liquid under pressure and which not only cleans the filter means at the periphery of the filter drum mechanically by means of a scraper or a brush, but which also ensures hydraulic cleaning by directing liquid under pressure on to the filter means. In particular, a cleaning procedure such as this can be recommended if the liquid to be purified has been discharged from the container, for example when an inspection of the container is to be made or when filter sludge has to be removed after the filtering apparatus has been in operation for an extended period.
The liquid container can be provided in the manner known in the art with an extractor device which is disposed at least in part under the filter drum, and by means of which the filter sludge which settles under the filter drum can be automatically removed from the container. The extractor device advantageously consists substantially of a scraper conveyor with conveying scrapers which can move along the container base and which entrain filter sludge, swarf and the like during their movement over the container base and which advantageously convey them via a ramp to an ejector device, where they are transferred to a contaminant vessel. In one particularly advantageous embodiment, the filter drum is provided at its bottom end face with an additional filter means, wherein the top belt of the scraper conveyor, with its conveying scrapers, is led past the additional filter means and thereby cleans the latter. Therefore, not only is the peripheral face of the filter drum used as a filter surface in this embodiment, but the bottom end face thereof is also used for this purpose, whereby an even higher liquid throughput can be achieved. In this embodiment also, the filter drum is fixedly disposed in the liquid container and can be withdrawn from the container from above or inserted therein from above without previously discharging the liquid to be filtered from the container.
Further features and advantages of the invention follow from the description given below and from the drawings, which illustrate an example of a preferred embodiment of the invention.